Nitrocellulose particles



United States Patent '0' NITROCELLULOSE PARTICLES John J. ONeill, Jr.,Alton, Ill., assignor to Olin Mathieson Chemical Corporation, EastAlton, 11]., a corporation of Virginia No Drawing. Application March 26,1956 Serial No. 573,585

' 2 Claims. (Cl. 1s-4s This invention relates generally to explosivesand more particularly to a method for making globular particles ofnitrocellulose of small granulation.

A process for making globular grains of smokeless powder base isdisclosed in US. Patent 2,027,114 granted to Olsen, Tibbitts and Kerone,January 7, 1936. The process disclosed in this patent is admirablysuited for making globular powder grains of the size ordinarily used aspropellants in small arms cartridges, i.e., Within the granulation ofabout 0.010 itch to about 0.025 inch, but it is unsuitable for makingproducts predominating in powder grains having a diameter of about 0.012inch or less. Particles of such small size are particularly advantageousfor use in molding large propellant grains and other articles fromnitrocellulose.

It is, therefore, an object of this invention to provide a method formaking particles of nitrocellulose in relaprovide a process for makingglobular nitrocellulose particles from fibrous nitrocellulose withoutcompletely destroying the fibrous structure of the nitrocellulose, theresulting globules being spheres of about 0.012 inch diameter or less.Another object is to provide a method for making substantially globularparticles of nitrocellulose particularly well suited for use in castinglarge propellant grains.

In accordance with this invention, the foregoing objects as well asothers are achieved, generally speaking, by suspending ungelatinizednitrocellulose fibers in a nonsolvent medium, dispersing a protectivecolloid in the resulting slurry, adding to the slurry at a predeterminedrate a solvent for the nitrocellulose which is substantially immisciblewith the non-solvent medium in sufiicient quantity to soften the fibersof nitrocellulose but to only It is essential that the fibers ofnitrocellulose be treated 1 with a protective colloid before suflicientsolvent is added to the slurry to soften the fibers, in order to avoidagglomeration of the softened fibers. Fibrous nitrocellulose must beused instead of gelatinized nitrocellulose in order to obtainnitrocellulose particles having the characteristics contemplated by thisinvention.

, The size distribution of the fibers of conventional nitrocellulosevaries from minute particles of about 0.0005 inch diameter to about0.020 inch long and 0.002 inch in cross-sectional diameter. A majorityof the fibers have dimensions of approximately 0.001 inch by 0.010 inch.In practicing this invention, a suitable protective colloid is added toa slurry of suci: fibers suspended in water or other suitablenon-solvent medium and the slurry is agitated until a protective coatingof the colloid is placed on 2,885,736 Patented May .12, 1959 each fiber.Solvent is then added slowly to the slurry as agitation is continued.The solvent may be ethyl acetate or any other solvent for nitrocellulosewhich is substantially immiscible with the non-solvent medium.Preferably, the solvent has a boiling point below that of thenon-solvent. Examples of suitable solvents in addition to ethyl acetateinclude methyl ethyl ketone, ethyl formate, butyl acetate and the like.A suitable mixture of solvent such as percent methyl ethyl ketone and 20percent toluene may also be used. The addition of solvent brings aboutsoftening of the minute particles which gradually assume a globularshape without complete gelatinization of the nitrocellulose as theslurry is agi: tated. The large fibers disintegrate under the influenceof agitation and the resulting smaller particles then assume asubstantially spherical shape.

The addition of solvent must be controlled in such a manner that theparticles 'of nitrocellulose are only softened and are rounded upwithout complete dissolution of the nitrocellulose, or, in other words,without the formation of a lacquer of the type formed by the processdisclosed in US. Patent 2,027,114. The particles having a fibrousstructure made by the process of this invention impart greater strengthto products molded therefrom than is imparted by completely gelatinizedparticles of nitrocellulose made by the process disclosed in US. Patent2,027,114. The solvent may be added to the slurry at any rate up to thepoint the slurry contains sufiicient solvent to begin softening thenitrocellulose. With a water-ethyl acetate system, this occurs whenabout 1.6 parts solvent per part of nitrocellulose are substantiallyuniformly distributed in from about 10 to about 17 parts water per partof nitrocellulose. The solvent concentration is then increased graduallyby adding solvent to the slurry at a rate of not more than about 0.25part solvent per one hundred parts of nitrocellulose per second. Undermost conditions, a final concentration in a waterethyl acetate system ofnot more than about two hundred parts solvent per one hundred parts ofnitrocellulose will be required to produce only partially gelatinizedglobular nitrocellulose particles of the type contemplated by thisinvention, but it has been found that as much as about three hundredparts solvent to one hundred parts nitrocellulose may be utilizedwithout the nitrocellulose becoming completely dissolved and coalescingto form a continuous lacquer phase of the type described in theaforementioned patent. This ratio may vary somewhat with other systemsbut in any system it is advantageous to utilize only that amount ofsolvent required to soften and not completely dissolve thenitrocellulsoe and less than that amount of solvent which will permitcoalescence. After the globules have assumed a globular shape, thesolvent is removed from the slurry by any suitable method such as bydistillation or by purging the slurry with air or other suitable gas.

Any suitable protective colloid may be utilized. For example, gum arabicor an animal glue such as Swifts Colloid No. 1 may be used to advantage.I

In order better to described and further clarify the invention, thefollowing is a detail description of a preferred embodiment thereof:

About parts by weight fibrous nitrated cotton linters having a nitrogencontent of about 12.6 percent and a viscosity of about 8 seconds asdetermined by the Hercules Falling Ball Method are slurried in about1500 parts water. About 50 parts by weight gum arabic are added to theslurry and the slurry is agitated until the fibers of nitrocellulose arecompletely coated with gum arabic. About one part by weight dinitrodiphenylamine is added.

The contents of the vessel are then heated to about 65 F. to 68 F. andabout 160 parts by weight ethyl acetate are added to the slurry.Agitation is continued until the solvent is substantially uniformlydispersed in the slurry. A total of about 140 parts ethyl acetate isthen added at a rate of about 0.25 part by weight per second whileagitation is continued for about 30 minutes or until the particles havea substantially globular shape. About 90 parts sodium sulfate dissolvedin about 300 parts water are added and agitation is continued until thesolution is substantially uniformly mixed with the slurry. Thetemperature of the slurry is raised to the boiling point and held atthis temperature until substantially all of the solvent has been removedtherefrom and the softened globules of nitrocellulose have becomehardened while retaining their globular shape. About 87 percent of theglobular particles of nitrocellulose thus obtained have a diameter ofabout 0.012 inch or less. About 77 percent of the particles have adiameter of 0.010 inch or less. About 46 percent of the particles have adiameter of 0.006 inch or less. About 37 percent have a diameter ofabout 0.005 inch or less and about 28 percent are about 0.004 inch orless in diameter. The globular shaped particles are only partiallygelatinized.

The foregoing procedure may be duplicated with the exception that afterabout 160 parts solvent have been added to the slurry of about 100 partsnitrocellulose and about 1500 parts water, additional solvent is addedat a rate of about 35 parts solvent per second until a total of about300 parts solvent have been added. Only about 52 percent of theresulting particles have a diameter of 0.012 inch or less, about 37percent are less than 0.010 inch in diameter, about 16 percent are lessthan 0.006 inch in diameter, about 13 percent are less than 0.005 inchin diameter, and about 11 percent are less than 0.004 inch.

When the foregoing procedure is followed with the exception that afterthe original 160 parts solvent have been added the rate of solventaddition is about 15 parts per second until a total of about 300 partsare added, the product contains about 50 percent globular particleshaving a diameter of about 0.012 inch or less, about 43 percent globularparticles having a diameter of 0.010 inch or less, about 32 percentglobular particles having a diameter of about 0.006 inch or less, about28 percent globular particles having a diameter of about 0.005 inch orless and about 26 percent particles of 0.004 inch or less diameter.

About 90 percent of the particles obtained in a typical batch of powdermade in accordance with the process of US. Patent 2,027,114 in which thesmokeless powder base is completely dissolved to form a lacquer and thislacquer is then comminuted into globules has a diameter of from about0.0248 to 0.0092 inch.

No definite theory as to the reason why the product of this invention ispredominately 0.012 inch or less in size has been forthcoming up to thistime. However, it is believed that because of the structure of thenitrocellulose each fiber breaks up into particles of the desired sizeas the fiber is softened by the solvent and because of the presence of afilm of a protective colloid on the surface of the fibers the resultingsmall particles do not coalesce. It appears, from the results of some ofthe experimental work that as the fiber is softened by the solvent abreak occurs at each node. In any event, the product obtained by theprocess of this invention consists predominately of only partiallygelatinized nitrocellulose particles having a maximum dimension of notmore than about 0.012 inch. Although the examples have been describedwith water as a non-solvent medium it is to be understood thatany othersuitable non-solvent for nitrocellulose can be utilized provided it issubstantially immiscible with the solvent for the nitrocellulose.

It is contemplated that the particles may be treated with anon-explosive plasticizer such as dibutyl phthalate, dinitrotoluene,diphenyl phthalate, diamyl phthalate, ethylcentralite or any otherdeterrent, if desired. Likewise, the particles maybe coated with anenergizing plasticizer such as a liquid nitric ester of a polyhydricalcohol including nitroglycerine, nitroglycol, or the like, as desired.Moreover, various modifying agents such as 'red lead oxide, Pb Olitharge, lead stannate, or other material which modifies the burningrate of powder grains may be placed on the surface of the particles ofnitrocellulose by any suitable method, if desired.

Although the invention has been described in considerable detail in theforegoing, it is to be understood that the purpose of such detail isonly for clarification of the invention and that many modifications canbe made by those skilled in the art without departing from the spiritand scope of the invention except as it is limited by the appendedclaims.

I claim:

1. A method for making substantially globular particles ofnitrocellulose having a diameter not substantially greater than 0.012inch which comprises forming a slurry by suspending fibers ofnitrocellulose in an aqueous medium in the ratio of about 1 part byweight nitrocellulose per 10 to 17 parts by weight aqueous medium,coating the fibers with a protective colloid, adding about 1.6

parts by weight ethyl acetate for each part by weight nitrocellulose,thereafter adding ethyl acetate to the slurry at a rate notsubstantially greater than about 0.25 part by weight per parts by weightnitrocellulose per second while maintaining the ethyl acetate tonitrocellulose ratio below about 3:1, agitating the slurry until thefibers have assumed a globular form, and removing the solvent from thenitrocellulose.

2. A method for making substantially globular particles ofnitrocellulose having a diameter not substantially greater than 0.012inch which comprises forming a slurry by suspending about 100 parts byweight fibrous nitrocellulose in about 1500 parts by weight of anaqueous medium, dispersing throughout the resulting slurry about 50parts by weight gum arabic, adding about 160 parts by weight ethylacetate, and subsequently adding an additional parts by weight ethylacetate at a rate of about 0.25 part per second, maintaining thesuspension by agitation for about 30 minutes, and removing the solvent.

References Cited in the file of this patent UNITED STATES PATENTS2,027,114 Olsen et al. Jan. 7, 1936 2,206,916 Olsen et al. July 9, 1940

1. A METHOD FOR MAKING SUBSTANTIALLY GLOBULAR PARTICLES OFNITROCELLULOSE HAVING A DIAMETER NOT SUBSTANTIALLY GREATER THAN 0.012INCH WHICH COMPRISES FORMING A SLURRY BY SUSPENDING FIBERS OFNITROCELLULOSE IN AN AQUEOUS MEDIUM IN THE RATIO OF ABOUT 1 PART BYWEIGHT NITROCELULOSE PER 10 TO 17 PARTS BY WEIGHT AQUEOUS MEDIUM,COATING THE FIBER WITH A PROTECTIVE COLLOID, ADDING ABOUT 1.6 PARTS BYWEIGHT ETHYL ACETATE FOR EACH PART BY WEIGHT NITROCELLULOSE, THEREAFTERADDING ETHYL ACETATE TO THE SLURRY AT A RATE NOT SUBSTANTIALLY GREATERTHAN ABOUT 0.25 PART BY WEIGHT PER 100 PARTS BY WEIGHT NITROCELLULOSEPER SECOND WHILE MAINTAINING THE ETHYL ACETATE TO NITROCELLULOSE RATIOBELOW ABOUT 3:1, AGITATING THE SLURRY UNTIL THE FIBERS HAVE ASSUMED AGLOBULAR FORM, AND REMOVING THE SOLVENT FROM THE NITROCELLULOSE.